PRENATAL GROWTH OF SPINAL CORD 67 



EXPLANATION OF FIGURES 



Figures 6 to 12 represent by curves the cross-sectional areas in each segment of 

 several embryonic and adult human spinal cords, as well as the corresponding 

 areas of gray and white matter (also the ependyma with the canal in figures 6 to 

 9). The curves are so plotted that the areas enclosed between the base-lines and 

 curves represent the total volumes of the cords and of their component parts, 

 respectively. The figures are so drawn that the areas representing the total vol- 

 umes of the cords are approximately the same. The lengths of the segments are 

 represented on the abscissa and so calculated that the total lengths of the various 

 cords are represented by the same length of abscissa. 



In any given figure, the changes in the height of the curves therefore represent 

 changes in the caliber of the cord as a whole (or in the relative amounts of its 

 component parts) at different levels. A comparison of the different figures shows 

 for the various stages the changes in the form of the cord as a whole, and in the 

 relative amounts of the component parts. The following points must be held in 

 mind to avoid error in comparing the various curves: 



1. Curves of figures 6, 7 and 8 are incomplete at the lower end. 



2. Curves of figures 9 and 10 are estimated at the upper end (dotted lines) as 

 explained in the text. 



3. The apparent increase at the upper end (all of the cervical region) of figure 

 6 is mostly due to the obliquity of the sections corresponding to the curvature of 

 the spinal cord. This also applies to the lower six thoracic segments of figure 6, 

 to the lumbar segments of figure 7, and to the upper four cervical, to some extent, 

 in figure 8. In figure 9, all the cervical segments are thus slightly enlarged, 

 although not enough to require dotted lines. 



I II Cervical viii i Thoracic 



Segments of spinal cord 



Fig. 6 Spinal cord of human embryo of 11 mm. 



